Gallium

Gallium,  ₃₁Ga

Pieces of gallium
General properties
Name, symbol	Gallium, Ga
Appearance	Silvery white
Gallium in the periodic table
Al ↑ Ga ↓ In Zinc ← Gallium → Germanium
Atomic number	31
Standard atomic weight (Ar)	69.723(1)
Group, block	(boron group); p-block
Period	period 4
Electron configuration	[Ar] 3d10 4s2 4p1
per shell	2, 8, 18, 3
Physical properties
Silvery-white
Phase	Solid
Melting point	302.9146 K ​(29.7646 °C, ​85.5763 °F)
Boiling point	2673 K ​(2400 °C, ​​4352 °F)
Density near r.t.	5.91 g/cm3
when liquid, at	6.095 g/cm3
Heat of fusion	5.59 kJ/mol
Heat of	256 kJ/mol
Molar heat capacity	25.86 J/(mol·K)
pressure
Atomic properties
Oxidation states	3, 2, 1, −1, −2, −4, −5​(an amphoteric oxide)
Electronegativity	Pauling scale: 1.81
energies	1st: 578.8 kJ/mol 2nd: 1979.3 kJ/mol 3rd: 2963 kJ/mol
Atomic radius	empirical: 135 pm
Covalent radius	122±3 pm
Van der Waals radius	187 pm
Miscellanea
Crystal structure	​Orthorhombic
Speed of sound thin rod	2740 m/s (at 20 °C)
Thermal expansion	18 µm/(m·K) (at 25 °C)
Thermal conductivity	40.6 W/(m·K)
Electrical resistivity	2.7·10-7 Ω·m (at 20 °C)
Magnetic ordering	Diamagnetic
Young's modulus	9.8 GPa
Poisson ratio	0.47
Mohs hardness	1.5
Brinell hardness	56.8–68.7 MPa
CAS Registry Number	7440-55-3
History
Naming	After Gallia (Latin for: France), homeland of the discoverer
Prediction	Dmitri Mendeleev (1871)
Discovery and first isolation	Lecoq de Boisbaudran (1875)

Gallium is a chemical element with symbol Ga and atomic number 31.

Properties

Chemical

Gallium is attacked by acids and free halogens, but does not react with air or water at room temperature, only at high temperatures, producing gallium(III) oxide Ga₂O₃. If Ga₂O₃ is reduced with elemental gallium in vacuum at 500-700 °C, it will yield the dark brown gallium(I) oxide, Ga₂O.

Ga₂O₃ + 4 Ga → 3 Ga₂O

Gallium(I) oxide is a strong reducing agent, capable of reducing sulfuric acid to hydrogen sulfide.

Gallium attacks most other metals by diffusing into their metal lattice. Aluminium is highly susceptible, as well as zinc, aluminium-zinc alloys, certain steel grades, making them very brittle.

Physical

Gallium is a soft silvery metal, brittle at low temperatures. If it is held in the human hand long enough, gallium will melt, since its melting point is 29.76 °C. Gallium expands by 3.1% when it solidifies, and therefore storage in either glass or metal containers should be avoided. Liquid gallium has a strong tendency to supercool below its melting point/freezing point. Unlike mercury, liquid gallium wets glass and skin, making it mechanically more difficult to handle. For this reason, as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers.

Availability

LED's contain a minute amount of gallium nitride, but the quantity is too small to be of importance. Certain low melting alloys contain gallium.

The best source of metallic gallium is GalliumSource, that sells gallium samples, a 100 g sample costs around 65$, though the price does not include shipping. For international shipping, the price is higher and the shipping is included in the price.

Preparation

Gallium can be prepared by reducing its halides.

Projects

• Inducing embrittlement in susceptible metals, such as aluminium
• Gallium nitride synthesis
• Gallium spoon prank
• Gallium beating heart
• Hydrogen generation

Handling

Safety

Pure gallium has little toxicity, but its tendency to wet most materials can be frustrating, so gloves should be worn when handling the pure metal, especially since it will melt in the hand if held too long. Some of its compounds have been shown to cause renal problems in tested animals. Bulk gallium nitride has been shown to be non-toxic and even bio-compatible.

Storage

Because gallium tends to expand when it solidifies, it's best stored in thick polyethylene bottles or if it's a small sample, in top lid boxes.

Disposal

Gallium is best recycled, when possible.

References

Relevant Sciencemadness threads

• Purifying Gallium